JP2000165907A - Device and method for recording color image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the high-quality printed result even on the border while preventing discontinuity caused by selectively using plural base color removal/ ink plate synthesis (CCR/BG). SOLUTION: A CRY value recognizing circuit 2 recognizes the position of C'M'Y' data, for which the colors of input RGB data are converted by a color converting circuit 1, in the color space for each dot and corresponding to the positions of C' M' Y' data in the color space, plural UCR/BG tables 5, 6 and 7 are selectively used. Thus, the tables are respectively optimized, the discontinuity generated on the border is corrected by a continuation table 4 and based on the recognition of C'M'Y' values by the CMY value recognizing circuit 2, the optimum table is automatically selected out of the plural UCR/BG tables 5, 6 and 7. In that case, the plural UCR/BG tables are synthesized by a UCR/BG synthesizing circuit 3 while utilizing the continuation table 4 and C'M'Y' is converted into CMYK while using the synthesized UCR/BG table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color image recording apparatus and a color image recording method for realizing high quality printing results.

[0002]

2. Description of the Related Art Conventionally, a color image recording apparatus and a color image recording method are generally known as UCR (Under Color Removal).
/ Undercolor removal / BG (Black Generation / Black plate synthesis).

[0003] For example, in the "image processing method" of Japanese Patent Application Laid-Open No. 2-9273 of the prior art 1, one line of RGB data as an input value is scanned in the main operation direction and the value of one line is integrated. The characteristics of the RGB values are obtained for each line, and UCR / BG is switched and used based on the characteristics.

[0004] Further, Japanese Patent Application Laid-Open No. 63-10089
Japanese Patent Application Laid-Open No. 5 (1999) discloses a method of correcting a UCR / BG value using a gamma table when converting a color space in an achromatic region.

[0005]

However, in general, input devices include a monitor, a scanner, a digital camera, and the like.
In many cases, colors are managed using a GB color space. On the other hand, many output devices, such as printers, manage colors using a CMYK color space. Therefore, it is necessary to convert the color space. Typically,
The conversion from RGB data to CMY data is a complementary color conversion,
This is performed by conversion using a color conversion table or the like. CM
When converting Y data to CMYK data, UCR
/ BG will be used. However, generally this U
The CR / BG is defined as one value or a table regardless of the position of the RGB value to be converted in the color space.

However, in practice, the value of UCR / BG is
Optimal values often differ depending on where the RGB values to be converted are located in the color space. Specifically, when the RGB values to be converted are close to achromatic colors, most of CMY is replaced with “K” (UCR / BG is 100%
Is desirable). Conversely, when the saturation of the RGB values to be converted is high, it is desirable to reduce the number of replacements with “K” (do not perform UCR / BG much).

Accordingly, U which optimizes an area close to an achromatic color
In the case where CR / BG is adopted, a result close to pure gray can be obtained by frequently using the K plate in an area close to an achromatic color. However, on the other hand, in a region with high saturation, the saturation decreases due to the heavy use of the K plate. Conversely, when UCR / BG that optimizes the high saturation area is adopted,
In a region with high saturation, replacement with the K plate is restricted. For this reason, a high saturation can be ensured, but in an area close to an achromatic color, replacement with the K plane is restricted. Therefore, it is necessary to express gray in CMY, which results in that pure gray printing cannot be obtained.

[0008] Japanese Unexamined Patent Publication No. 2-9273 of the prior art 1 is similar to the present invention in that a plurality of UCRs / BGs are prepared and selectively used according to the characteristics of RGB. However, the means for recognizing RGB characteristics scans one line in the main operation direction of the scanner and integrates the values to recognize the RGB characteristics for each line. In this case, even if there is a change in RGB characteristics such that an achromatic color and a high-saturation color are mixed in one line, integration processing is performed. As a result, accurate characteristics cannot be determined as a result. In addition, when a plurality of UCRs / BGs are properly used, discontinuity occurs at a boundary, but the correction is not mentioned.

Japanese Unexamined Patent Publication No. 63-100895 of the second prior art discloses that when performing achromatic conversion, gamma correction of UCR / BG is performed to obtain a print result close to pure gray. However, since the K version is not frequently used when expressing an achromatic color, it is practically impossible to realize a pure gray color.

An object of the present invention is to provide a color image recording apparatus and a color image recording method which prevent discontinuity caused by selectively using a plurality of UCRs / BGs and realize high quality printing results even at boundaries. Aim.

More specifically, the present invention is required when converting values of RGB data, which is a color space of an input device, into CMYK data, which is a color space of an output device.
A plurality of UCRs / BGs are provided, and color conversion is performed using an optimum UCR / BG for each RGB value to be converted. Accordingly, it is an object to provide a color image recording apparatus and a color image recording method that perform optimal conversion in all color spaces and realize high quality printing results.

[0012]

According to a first aspect of the present invention, there is provided a color image recording apparatus, comprising: a pixel value for recognizing a position in a color space of input RGB pixel data for each dot; A recognition circuit, a plurality of conversion tables for optimizing each of the pixel data corresponding to the position of the color space, and a plurality of conversion tables based on the recognition of the pixel data value by the pixel value recognition circuit. And a synthesizing circuit for selecting and synthesizing the most suitable conversion table, and converting the pixel data into CMYK data using the conversion table synthesized by the synthesizing circuit.

In the invention according to claim 2, the color image recording apparatus may further include a continuity table for correcting a discontinuity occurring at a boundary between a plurality of conversion tables.

According to a third aspect of the present invention, the pixel value recognizing circuit according to the first or second aspect is an RGB value recognizing circuit for recognizing an RGB value.
This is an LUT table for optimizing each of the RGB values in accordance with the position of the color space. A LUT synthesis circuit for selecting and synthesizing a table, and using the LUT table synthesized by the LUT synthesis circuit to convert RGB data into CM
It is good to convert to YK data.

According to a fourth aspect of the present invention, the pixel value recognizing circuit according to the first or second aspect includes a color conversion circuit for performing color conversion of RGB pixel data into C′M′Y ′ data, and a color conversion C And a CMY value recognition circuit that recognizes the position of the 'M'Y' data in the color space for each dot. The conversion table stores the C'M'Y 'data in the color space. A plurality of under-color removal (UCR) / black plate combination (BG) tables for respectively optimizing correspondingly, the combination circuit based on the recognition of C'M'Y 'data values by the CMY value recognition circuit. Is a UCR / BG synthesizing circuit for automatically selecting and synthesizing an optimum UCR / BG table from the UCR / BG tables of the above, and using the UCR / BG table synthesized by the UCR / BG synthesizing circuit to perform C'M 'Y' data to CMYK data It is preferable to conversion.

According to a fifth aspect of the present invention, there is provided a color image recording method, comprising: a pixel value recognizing step of recognizing a position of input RGB pixel data in a color space for each dot; A table creation step of creating a plurality of conversion tables for optimizing each of them, and automatically selecting an optimal conversion table from the plurality of conversion tables based on recognition of pixel data values by a pixel value recognition process. And a table synthesizing step of synthesizing, and converting the pixel data into CMYK data using the conversion table synthesized by the table synthesizing step.

In the invention described in claim 6, the color image recording method preferably further includes a step of creating a continuity table for correcting discontinuity occurring at a boundary where a plurality of conversion tables are used.

In the invention according to claim 6, the pixel value recognition step according to claim 5 or 6 is an RGB value recognition step for recognizing as an RGB value, and the table created in the table creation step is a color space of RGB values. Is an LUT table for optimizing each of the LUT tables corresponding to the positions of the LUTs. The synthesizing process automatically selects an optimum LU from a plurality of LUT tables based on the recognition of the RGB values in the RGB value recognition process.
This is an LUT synthesis process for selecting and synthesizing a T table.
The RGB data may be converted to CMYK data using the LUT table synthesized by the UT synthesis process.

According to an eighth aspect of the present invention, in the pixel value recognizing step according to the fifth or sixth aspect, the color conversion step of performing color conversion of RGB pixel data into C′M′Y ′ data and the color-converted C And a CMY value recognition step of recognizing the position of the 'M'Y' data in the color space for each dot. The conversion table created in the table creation step is C'M'Y '. There are a plurality of under color removal (UCR) / black plate synthesis (BG) tables for optimizing each corresponding to the position of the data color space. The synthesis process is C'M'Y 'data by the CMY value recognition process. Optimum UC automatically from multiple UCR / BG tables based on value recognition
This is a UCR / BG synthesizing step of selecting and synthesizing an R / BG table.
Convert C'M'Y 'data to C using CR / BG table
It is good to convert to MYK data.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a color image recording apparatus and a color image recording method according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 6 show an embodiment of a color image recording apparatus and a color image recording method according to the present invention.

The first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the first embodiment of the present invention. This embodiment will be described below with reference to FIG.

The color image recording apparatus according to the first embodiment shown in FIG. 1 has a color conversion circuit 1, a CMY value recognition circuit 2, a UCR
/ BG synthesis circuit 3, a continuation table 4, and UCR / BG tables 5, 6, and 7.

The color conversion circuit 1 is a circuit that performs color conversion of RGB data input from an input device into C′M′Y ′ data.

The CMY value recognition circuit 2 is a circuit for recognizing the position in the color space of the C'M'Y 'data color-converted by the color conversion circuit 1 for each dot.

The UCR / BG synthesizing circuit 3 automatically selects an optimum table from among a plurality of UCR / BG tables 5, 6, 7 based on the recognition of C'M'Y 'data values by the CMY value recognizing circuit 2. Is a circuit for selecting and synthesizing.

The continuation table 4 includes a plurality of UCR / BGs.
This is a table for continuity processing for correcting discontinuities occurring at boundaries by properly using tables 5, 6, and 7.

The UCR / BG tables 5, 6, and 7 are C '
A plurality of under color removal (UCR) / black plate synthesis (B) for optimizing each corresponding to the position of the color space of M'Y 'data
G) Table.

In general, many input devices use an RGB space as a color space, such as a monitor, a scanner, and a digital camera. On the other hand, an output device such as a printer uses a CMYK space as a color space. Therefore, upon output, the RGB data is converted to CMY
A need arises to convert the color space to K data. At that time, a color conversion table called an LUT (logical unit table / theoretical device table) is used for color conversion, and R
A method of directly converting GB data to CMYK data is also conceivable. However, in the first embodiment, in order to perform more advanced color management, RGB data is converted into C′M′Y ′ data once, and then C′M ′
A method of converting Y ′ data into CMYK data is employed. In the first embodiment, the RGB data has 8-bit gradation and takes a value from 0 to 255.

The color conversion circuit 1 converts the RGB data into C'M '
A circuit for converting into Y ′ data is shown. As a method of converting RGB data to C′M′Y ′ data, a simple complementary color conversion shown below and a method of performing conversion by referring to an LUT are conceivable, but in the present invention, only one method is used. Not done.

The complementary color conversion is performed based on the following equation. C ′ = 1−R M ′ = 1−G Y ′ = 1−B

The input RGB data is converted by the color conversion circuit 1 into C′M′Y ′ data. Converted C '
The MMY data is determined by the CMY value recognition circuit 2 for each dot at which position in the CMY space. In order to make the determination, the CMY value recognition circuit 2
Calculate the following values.

K = min (C ′, M ′, Y ′) a = max (C ′, M ′, Y ′) − min (C ′,
M ', Y')

The “k” calculated here is C′M ′
It is sent to the UCR / BG synthesis circuit 3 together with the Y 'value. Also, “a” is sent to the continuation table 4. Based on these values, the UCR / BG combining circuit 3 determines UCR / BG.

The following equation is used to convert C'M'Y 'data to CMYK data using UCR / BG. Although UCR / BG is represented by a table, it can be regarded as a function related to the above “k”,
They are represented as CR (k) and BG (k).

C = C'-UCR (k) M = M'-UCR (k) Y = Y'-UCR (k) K = BG (k)

Note that UCR (k) and BG (k) are UC
The R / BG combining circuit 3 combines the optimized UCR / BG tables 5, 6, and 7 for each existing position of the C'M'Y 'data values in the CMY space before the combination. Will be described.

FIG. 2 shows an example of the configuration of the characteristics of the UCR / BG table 5. Actual UCR / BG table values greatly depend on the characteristics of output devices such as printers to be used.
For this reason, it cannot be decided unconditionally. FIG. 2 is a general example. Here, the UCR / BG table 5 is assumed to be a table optimized for an achromatic region.
In other words, the table is optimized for the case where the value of “a” is small. FIG. 2 shows a case where 100% UCR / BG is performed on the above “k”. This is because it is desirable that the achromatic region be represented only by the K plane. The UCR defined here is UCR1 (k), and the BG is BG1 (k).

FIG. 3 shows a configuration example of the UCR / BG table 6. The UCR / BG table 6 shown here is assumed to be a table optimized for an intermediate region between an achromatic color and a region with high saturation. UCR defined here
Is UCR2 (k), and BG is BG2 (k).

FIG. 4 shows a configuration example of the UCR / BG table 7. The UCR / BG table 7 is assumed to be a table optimized for an area with high saturation. In FIG. 4, both the removal of the CMY value by the UCR and the generation of the K version by the BG for the above “k” are restricted.
The settings are such that the saturation is not reduced due to mixing of plates. The UCR defined here is UCR3 (k), and the BG is BG3 (k).

These three UCR / BG tables are
It is synthesized by the CR / BG synthesizing circuit 3. The algorithm at the time of synthesis is shown below.

UCR (k) = (1-b1) × UCR1
(K) + b1 × UCR2 (k) −b2 × UCR2 (k)
+ B2 × UCR3 (k)

BG (k) = (1−b1) × BG1 (k)
+ B1 × BG2 (k) −b2 × BG2 (k) + b2 × B
G3 (k)

Here, the codes b1 and b2 are obtained by receiving “a” generated by the CMYK recognition circuit 2,
It means a value generated by the continuation table 4.

FIG. 5 shows a specific example of the continuation table 4. The continuation table 4 uses “a” as an input value,
B1 and b2 having values of 0 to 1 are generated. Referring to FIG. 5, when “a” is small, that is, for a color in an area close to an achromatic color, b1 and b2 are both 0, and when “a” is large, that is, for a color in a high saturation area, b1 , B2
It turns out that both become 1. This value is referred to as the above UCR (k),
When applied to BG (k), UCR1 (k), which is a UCR / BG optimized for achromatic color, in a region close to achromatic color
BG1 (k) is applied, and in a high-saturation region, UCR3 which is a UCR / BG optimized for a high-saturation color
(K) and BG3 (k) are applied. Since b1 is 1 and b2 is 0 in the region of the intermediate color, UCR2 (k) and BG2 (k) optimized for the intermediate color are also applied. As for the boundary, values b1 and b2 that are properly balanced by the value of “a” are given, and
Two UCR / BG tables can be combined in a well-balanced manner, and discontinuities at boundaries can be eliminated.

Using the above UCR / BG, C'M'Y '
Is converted to CMYK and printed by the output device.

According to the above embodiment, the color conversion circuit 1 for color-converting the RGB data input from the input device into C'M'Y 'data is provided. A CMY value recognition circuit 2 for recognizing the position of the 'Y' data in the color space for each dot;
A plurality of UCR / BG tables 5, 6, and 7, each of which is optimized according to the position of the color space of the data, have a plurality of UCR / BG tables. The CMY value recognition circuit 2 has a continuity table 4 which is a table for correction.
Based on the recognition of the M'Y 'value, an optimum table is automatically selected from a plurality of UCR / BG tables 5, 6, and 7, and a continuous table is formed so that no discontinuity occurs at the boundary. UCR / BG synthesizing circuit 3 for synthesizing a plurality of UCR / BG tables using the UCR / B
Using the UCR / BG table synthesized by the G synthesizing circuit 3, C'M'Y 'is converted into CMYK.

C′M ′ converted by the color conversion circuit 1
The presence position of the Y ′ data in the CMY color space is determined by the CMY recognition circuit 2 for each dot. The plurality of UCR / BG tables 5, 6, and 7 are optimized according to the position characteristics in the CMY color space. In particular,
UC optimized for achromatic regions in color space
An R / BG table, a UCR / BG table optimized for a region with high saturation in the color space, and the like.

The UCR / BG synthesizing circuit 3 selects an optimum UCR / BG table from a plurality of UCR / BG tables 5, 6, 7 based on the judgment result of the UCR value recognition circuit 2. As a result, in the achromatic region, the UCR / BG table that actively replaces the K plate is selected, and a print result close to pure gray can be realized.
In a high-saturation area, a high-saturation printing result can be realized by limiting the replacement with the K plate.

When a plurality of UCR / BG tables are properly used, discontinuity occurs at a boundary. However, the discontinuity is corrected by synthesizing the UCR / BG table using the continuation table 4. You can do it.

Next, a second embodiment of the present invention will be described.
This will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration example of the second embodiment.

The color image recording apparatus according to the second embodiment shown in FIG. 6 has a continuation table 4, an RGB value recognition circuit 8,
It has a UT synthesis circuit 9 and LUTs 10, 11, and 12.

The color image recording apparatus of the second embodiment directly converts RGB data into C
This is converted into MYK data. In this case, the RGB data value of the input signal is calculated by the RGB value recognition circuit 8.
The existence position in the RGB space is recognized. in this case,
The processing procedure is as follows.

K = min (R, G, B) a = max (R, G, B) -min (R, G, B)

In this case, the LUTs 10, 11, 12
Shows a color conversion table in consideration of the respective characteristics of the RGB values, and this table is synthesized by the LUT synthesis circuit 9. The algorithm is as follows.

LUT = (1−b1) × LUT1 + b1 ×
LUT2-b2 × LUT2 + b2 × LUT3

As a result, an optimized LUT is selected for each value of RGB data, and the same effect as in the case of optimizing UCR / BG can be obtained.

The above embodiment is an example of a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, in the above embodiment, UC
Although the case where three R / BG tables are provided has been described, the present invention is not limited to this.

[0058]

As is apparent from the above description, the color image recording apparatus and the color image recording method of the present invention recognize the position of the pixel data input from the input device in the color space for each dot. By using a plurality of conversion tables, each of which is optimized in accordance with the position of the pixel data in the color space, the discontinuity occurring at the boundary is corrected. In addition, based on the recognition of the pixel values, an optimum table is automatically selected from a plurality of conversion tables, and a continuation table is used so that discontinuity does not occur at a boundary at that time. The conversion table is synthesized, and the pixel data is converted into CMYK using the synthesized conversion table.

Therefore, the UCR / B depending on the area of the color space
Since differences in characteristics such as G can be managed individually, optimization can be performed for each of them, and print quality improves. For this reason, color reproducibility is improved. Since achromatic colors can be printed using the K plate frequently, natural colors can be expressed, and the use of the K plate can be restricted for highly saturated colors.
For this reason, printing with high saturation can be realized, and the contrast is improved. Further, a discontinuous point generated when a plurality of UCRs / BGs are switched and used can be corrected, and stable print quality can be secured.

[Brief description of the drawings]

FIG. 1 is a processing block diagram showing a first embodiment of a color image recording apparatus and a color image recording method of the present invention.

FIG. 2 UCR / BG optimized for achromatic regions
It is a figure showing a characteristic.

FIG. 3 shows a UCR / BG optimized for an intermediate color region.
It is a figure showing a characteristic.

FIG. 4 UCR optimized for highly saturated color regions
FIG. 9 is a diagram showing / BG characteristics.

FIG. 5 is a diagram showing a specific example of a continuation table.

FIG. 6 is a processing block diagram illustrating a second embodiment.

[Explanation of symbols]

Reference Signs List 1 color conversion circuit 2 CMY value recognition circuit 3 UCR / BG synthesis circuit 4 continuity table 5, 6, 7 UCR / BG table 8 RGB value recognition circuit 9 LUT synthesis circuit 10, 11, 12 LUT (logical unit table / theoretical) Equipment table)

Claims (8)

[Claims] 1. A pixel value recognizing circuit for recognizing a position of input RGB pixel data in a color space for each dot, and a plurality of pixel value recognizing circuits for optimizing each of the pixel data corresponding to the position of the pixel data in a color space A conversion table, and a synthesizing circuit for automatically selecting and synthesizing an optimal conversion table from the plurality of conversion tables based on recognition of the pixel data value by the pixel value recognition circuit, and synthesizing by the synthesizing circuit. A color image recording apparatus for converting the pixel data into CMYK data using the converted conversion table. 2. The color image recording apparatus according to claim 1, wherein the color image recording apparatus further includes a continuity table for correcting a discontinuity occurring at a boundary where the plurality of conversion tables are used. . 3. The pixel value recognizing circuit is an RGB value recognizing circuit for recognizing an RGB value, and the plurality of conversion tables are LUT tables for optimizing each of the plurality of conversion tables in accordance with a position of the RGB value in a color space. Wherein the synthesis circuit is an LUT synthesis circuit for automatically selecting and synthesizing an optimum LUT table from the plurality of LUT tables based on the recognition of the RGB values by the RGB value recognition circuit; 3. The color image recording apparatus according to claim 1, wherein the RGB data is converted into CMYK data using an LUT table synthesized by the above. 4. A color conversion circuit for color-converting RGB pixel data into C′M′Y ′ data, and the pixel value recognition circuit sets the position of the color-converted C′M′Y ′ data in a color space by one. And a CMY value recognition circuit for recognizing each dot. The conversion table includes a plurality of CMY value recognition circuits for optimizing the C′M′Y ′ data in accordance with the position of the color space. It is an under color removal (UCR) / black plate composition (BG) table, wherein the composition circuit is C'M 'by the CMY value recognition circuit.
The plurality of UCR / BGs based on the recognition of the Y 'data value.
A UCR / BG synthesizing circuit for automatically selecting and synthesizing an optimum UCR / BG table from the tables, and a UCR / BG synthesized by the UCR / BG synthesizing circuit.
Using the BG table, convert the C'M'Y 'data into CM
3. The color image recording apparatus according to claim 1, wherein the color image recording apparatus converts the color image data into YK data. 5. A pixel value recognizing step of recognizing a position of input RGB pixel data in a color space for each dot, and a plurality of pixel values for optimizing each of the pixel data in accordance with the color space position of the pixel data. A table creating step of creating a conversion table; and a table combining step of automatically selecting and combining an optimal conversion table from the plurality of conversion tables based on recognition of pixel data values in the pixel value recognition step. And a step of converting the pixel data into CMYK data using a conversion table synthesized in the table synthesizing step. 6. The color image recording method according to claim 5, further comprising a step of creating a continuity table for correcting a discontinuity occurring at a boundary where the plurality of conversion tables are used. Color image recording method. 7. The pixel value recognizing step is an RGB value recognizing step of recognizing as an RGB value. A table created in the table creating step is optimized for each of the RGB values in a color space position. Wherein the synthesizing step is an LUT synthesizing step of automatically selecting and synthesizing an optimum LUT table from the plurality of LUT tables based on the recognition of the RGB values by the RGB value recognition step, 7. The color image recording method according to claim 5, wherein the RGB data is converted into CMYK data using an LUT table synthesized by an LUT synthesis step. 8. The pixel value recognizing step includes a color converting step of performing color conversion of RGB pixel data into C′M′Y ′ data, and setting a position of the color-converted C′M′Y ′ data in a color space by one. And a CMY value recognition step of recognizing each dot. The conversion table created in the table creation step corresponds to the position of the C′M′Y ′ data in the color space. A plurality of under color removal (UCR) / black plate combination (BG) tables for optimization, wherein the combination step is C'M 'by the CMY value recognition step.
The plurality of UCR / BGs based on the recognition of the Y 'data value.
A UCR / BG synthesizing step of automatically selecting and synthesizing an optimal UCR / BG table from the tables, and a UCR / BG synthesized by the UCR / BG synthesizing step.
Using the BG table, convert the C'M'Y 'data into CM
7. The color image recording method according to claim 5, wherein the color image is converted into YK data.